The present invention is related to wireless networks, and in particular to wireless local area networks (WLANs).
Wireless networks, e.g., local area wireless networks conforming to the IEEE 802.11 standard have become common. WLANs often are used in infrastructure mode with one wireless station, called an access point (AP), acting as a base station for a set of client wireless stations. A client station associates with an AP, and following such association, all wireless communication between the client station and any other entity is via the AP. In such a WLAN, there may be times when it is necessary or desired to take an AP of a WLAN offline while the AP is operating, e.g., while there are one or more operational client stations that are currently associated with the access point. Furthermore, there may be a need to take the access point offline in an manner that does not interrupt communication between a client of the AP and another part of the network to which the AP is connected. For example, some of the operating client stations of the AP may be using the communication for live voice communication using, e.g., voice over IP (VoIP), and in such a case it would be detrimental to interrupt a live voice communication.
A forced handoff from one base station of a cellular wireless system to another is well known in the art. For example, it is known how to take a base station of a cellular telephone system offline in a cellular system. In a CDMA cellular system, it is also known how to carry out what is called a “soft handoff” that provides for handing off a particular handset in communication from one base station to another in a manner that does not interrupt communication. See for example, Wong, D.; Teng Joon Lim: “Soft handoffs in CDMA mobile systems,” IEEE Personal Communications, Vol. 4, No. 6, Pages: 6-17, December 1997. See also Tripathi, N. D.; Reed, J. H.; VanLandinoham, H. F.: “Handoff in cellular systems, IEEE Personal Communications, Vol. 5, No. 6, Pages: 26-37, December 1998, and Seen-Ho Hwang; Seong-Lyun Kim; Hyun-Seo Oh; Chang-Eon Kang; Jung-Young Son: “Soft handoff algorithm with variable thresholds in CDMA cellular systems,” Electronics Letters, Vol. 33, No. 19, 11, Pages: 1602-1603, September 1997.
As WLANs originally designed for data communication are oriented more and more to real time applications, such as wireless VoIP and other wireless media services, there are higher requirements being made on wireless network service availability and reliability. For example, there is an expectation of non-interrupted voice service to a similar level to that achieved with a wired phone call. In a widely deployed wireless network environment, there may be a need to pull a wireless AP out of service, temporarily or permanently. Reasons for such action may be a service quality problem, need for a system upgrade, or for administrative purposes. With present technology, the clients attached to the AP may lose ongoing services, especially in the case of real time applications. Thus, with VoIP, a call may be dropped, or service quality may otherwise be degraded.
Thus there is a need in the art for taking an AP offline without dropping service, including communication with one or more client wireless stations. There furthermore is a need to prevent new clients from associating with the AP.
In cellular telephony, each cell has a base station, and the mobile stations communicate via the base station of the cell. When a cell needs to go down, methods are known and used in cellular telephony that force a mobile station to handover to another base station if the mobile station is in an active call state with the base station that's about to be taken offline. This is carried out typically by the base station instructing the mobile station to hand over to a specific cell, e.g., a specific base station. A base station being taken off line instructs its mobile stations to so hand over, one mobile station at a time.